This project tests the Dilution Effect hypothesis, which predicts that parasite success should be inversely related to the number of species in a community of host organisms. The hypothesis will be tested in a model system of mosquito larvae that breed in containers, and a parasite that infects them. The number of host species will be modified and the success of the parasite will be measured. The prevalence of parasites in natural larval habitats will be quantified and the relationship between parasite prevalence and the number of species of mosquito larvae will be tested. PUBLIC HEALTH RELEVANCE: This project addresses whether parasites succeed at reduced rates within more diverse communities of host organisms, a theory known as the host Dilution Effect. The hypothesis will be tested in communities of mosquito larvae that breed in containers, studying a parasite that infects those larvae. The number of host species will be modified and the success of the parasite will be measured. The prevalence of parasites in natural larval habitats will be quantified and the relationship between parasite prevalence and the number of species of mosquito larvae will be tested. Additional experiments are designed to test various hypotheses about the mechanism of host dilution, as well as the role of parasitism in affecting competition among hosts. The project is relevant to public health from the perspective of managing risks through the management of biodiversity in the human environment. Also, the project investigates species interactions involving mosquitoes, which are vectors of numerous diseases in humans, including several encephalitis viruses, Chikungunya virus, yellow fever, dengue, and West Nile virus. Understanding parasite regulation of these vectors may improve our ability to control disease vectors.